LUCENE-6852: merge trunk

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene6852@1710430 13f79535-47bb-0310-9956-ffa450edef68
tree: d4860be38d53a4fc0d81a74f3e2af291133c5977
  1. dev-tools/
  2. lucene/
  3. solr/
  4. .gitignore
  5. .hgignore
  6. build.xml
  7. README.txt